Whisk together sugar and egg yolks only (*gently whisk the whites and set aside for later). Then whisk in milk and butter
In a separate bowl, combine flour, baking powder and salt
Add the dry ingredients to wet and mix until well combined. Fold in egg whites (until combined but not over mixed)
Line 12 muffin slots with silicone liners & add 3 tbsp batter in each. Add 1 tsp cinnamon sugar filling, then top with 2 tbsp of batter & sprinkle remaining cinnamon sugar on top
Bake at 375 degrees for 18-20 minutes
Let cool, top with cream cheese frosting & enjoy :)